The nature of the population for open heart surgery is rapidly changing; in recent years, an increasing number of high risk patients are being brought to the operating table for this procedure. There are a number of reasons for this.
In general, such patients are substantially older than before. Specifically, the mean age is approximately seventy-one years while, only twelve years ago, the mean age was only fifty-one years. In essence, the problems arise as a result of the success of other treatments. Improvements in medical treatment have resulted in the availability of a wide range of cardiac drugs which will prevent angina, thereby permitting patients to survive longer, even though heart problems are present. In addition, angioplasty and arterectomy of single, double, and even multiple vessels are commonplace; thus, many patients come to surgery only after several other cardiac procedures have been carried out. In addition, the percentage of second operations performed on the same patient is also increasing. In some areas, it is as high as 10% to 30%; this is because patients are surviving longer after the first operation.
Thus, patients seeking open heart surgery are much sicker and frailer than they ever were. They present higher risks and, of course, increased anxiety on the part of both the patient and the surgeon. Hence, the use of such expedients as the intra-aortic balloon has been rising steadily. This device is used to assist, on a temporary basis, the failing heart after surgery is completed.
In almost every case of coronary artery bypass surgery, the internal mammary artery (IMA) is used. This artery tends to become narrower when the blood pressure falls just after all the grafts have been anastomosed and the aortic cross pump removed. This phenomenon is called arterial spasm. This is extremely detrimental to the patient since it does not permit good perfusion of the left heart, thus reducing blood pressure even further. The fact that the IMA is usually implanted in the left anterior descending artery of the heart is a contributing factor. A vicious cycle is created and must be treated immediately by insertion of an Intra-Aortic Balloon Pump (IABP), drugs, or even the insertion of an additional graft, taken from the saphenous vein, into the left anterior descending artery. If treatment is not carried out promptly, the patient may die.
A further problem resides in the age of the patients and the condition of their arteries. It is common to find diffuse atherosclerosis in such patients, as well as aortas which are seeded with calcified plaque. Thus, the risk of stroke is substantially increased because, if a small piece of calcium is dislodged, it can easily be carried to the brain as an embolism through, for example, the brachiocephalic artery. This can occur as a direct result of certain mechanisms; specifically, cross clamping of the ascending aorta to isolate and cool the heart for the surgery. Another cause is the jet of blood exiting from the aortic cannula which can, if it impinges on the walls of the aorta, dislodge plaque therefrom, especially in the region of the aortic arch. Moreover, this area generally has greater calcium deposits than any other part of the aorta.
Many of the patients suffer from peripheral atherosclerosis, wherein the femoral arteries are extremely narrowed or even fully occluded. This condition makes the introduction of the IABP through that artery virtually impossible or, at best, at high risk with a strong likelihood of complications. There also are occasions when heart failure occurs under conditions such that the IABP and drugs are insufficient to maintain the patient. In such situations, an extra-aortic pump (EAP), particularly one which will be activated and controlled by the existing IABP console, can be effective. While the IABP can increase coronary blood flow by 5% to 15% the EAP can increase the flow by 100% or more.
Still another problem relates to the perioperative monitoring of the patient's blood pressure. This can be extremely difficult, and sometimes even impossible, the use of either the radial or femoral artery.